Magnetic bucking bar



- Oct. 10, 1944.

w. R. HOLCOMB MAGNETIC BUCKING BAR Fild July 25, 1940 IN VENTOQ PatentedOct. 10, 1944 MAGNETIC BUCKING BAR William Ray Holcomb, Burbank, Calif.,assignor to Lockheed'Aircraft Corporatiom Burbank,

Calif.

Application July 23,1940, Serial No. 346,911 J Claims. -.(Cl. 78-48)This invention relates to an improved apparatus and method for headingrivets in confined places inaccessible to manually held bucking bars orrivet squeezing machines.

With the development of skin stressed metal aircraft, riveting of theskin to structural or other members, especially at the nose and trailingedge of the wing, has become a difiicult process. With the advent ofintegral fuel tanks utilizing the skin structure as part thereof itbecomes-increasingly difiicult to reach both ends of the rivets, as isnecessary to properly set up a rivetby means of a riveting hammer and amanually held bucking bar. There is a practical limit as to how far anoffset bucking bar can be held firmly enough to produce a ound rivethead; the modern use of relatively large skin sheets backed by closelyspaced or continuous corrugated longitudinals, and the addition of aninner skin for various purposes, has added to the difficulties inproducing acceptacle riveting on a pro-.

duction basis.

It is accordingly an object of this invention to'provide a novel form ofbucking bar that can'be inserted in cramped quarter andv maneuvered intoposition from an opening some distance away, the bar being brought intoand held in operative position against the end of the rivet by a magnetapplied to the external surface of the object being riveted.

'It is also an object of this invention to provide a magnetically heldbucking bar in combination with a magnet associated with a rivetinghammer. so arranged that the magnet will draw up and hold the buckingbar in position on the back or inner side of the work, while theriveting hammer sets and forms the rivet inthe usual manner.

It is a further object of thi invention to provide a combined rivetinghammer and magnet for the purpose described, the magnet having a polevor shoe formed as an annular surface coaxial with and embracing thehammer-to hold the latter accurately at right angles to the surface ofthe work to assure truly positionedrivet heads in the ease of both flushand round headed.

rivets.

Other and further important objects of this the line I-I of Figure II,of an airplane wing structure, for illustrative purposes.

Figure II is a view at right angles to the showing of Figure I,comprising a traverse section of the wing structure.

Figure III embodiesa modified form of bucking bar suitable for use inriveting wing reinforcingmembers of continuous corrugated form.

Asshown:

In-orderto illustrate a form of this invention adapted for a particulartype of work, an airplane wing structure has been chosen-for descriptivepurposes. Anouter skin Ill is to be riveted to the flanges H of a series.of channel members 12, which in turn may have an inner skin or liningl3 riveted to the inner flanges .14 thereof; As shown in Figure III, thechannel members l2 may be replaced by'a corrugated reinforcing sheet l5.The details of such airplane structures form-no part of the presentinvention, and it is contemplated that-the bucking bar will be so formedas to be readily inserted and. moved 1 throughout the length of thespaces available behind the surfacawhich spaces may extend for a numberof feet, limited only by the size of commercially available sheetmaterial. It will be evident that the usualtype of hand held bucking baror rivet squeezing machine cannot reach several feet-into such smallspaces. Other examples of inaccessible riveting locations in airplaneconstruction will -'readily occur to those skilled in the art; such asthe nose and trailing edges of the wings, for example.

As disclosed herein, the skin I0 and channel flange it are perforatedand dimpled for the'insertion of countersunk head rivets Hi. Thisinvention is not limited to that type of rivet however as other types ofrivets can be set equally well, if necessary by theprovisionof suitableshaped recesses in the hammer and bucking bar as is common'p-racticewith hand held tools.-

The bucking bar of this invention comprises a holder l7 shaped'ingeneral to fit the space available,- and a magnetically responsivemovable member guided by the holder l1. As shown in Figures I-and II theholder I1 is centrally recessed to-receive the bucking bar member 18,which latter carries guiding tongues 19 slida-ble in slots in the sidepieces 20 of the holder, pins 2| serving to limit the outward movementof the member I8, to leave space for the desired thickness of rivethead. The upper ends of the side pieces 20 are grooved at 22 to-passover already formed rivet heads. The holder, may be conveniently shiftedalong ,the .channel member 12 by means 011a long flexible shaft23,"whichcan be operated om o n end f t c an e or thro hand. .hole .orinspectionopening at, some distance from the desired rivet location.While the flexible shaft can be marked to closely approximate thelocation of the bucking bar, which can also be seen through the rivetholes, it is also possible to feel for the bucking bar by means of asmall permanent horseshoe magnet, the two poles of which will accuratelylocate or define the edges of the bucking bar by variations in theattraction on the magnet when the materials being Worked on lackmagnetic response; as in the case of aluminum alloys, and non-magnetictype of stainless steel for example.

A powerful electromagnet 24 is combined with an air operated rivetinghammer 25, the magnet having an annular pole piece 26 which is pressedagainst the outside skin l and serves, when the magnet is energized, todraw the member l8 to its limit of travel in the holder, also causingthe side members 26 of the holder to press the channel flange l2 againstthe skin ID.

A tappet 21 for the air hammer 25 has an enlarged head 28 countersunk inthe annular magnet pole piece 26,'the surface of the head 28 being flushwith the end of the pole piece, in this case of flush rivets, and ofconsiderably greater diameter to produce a truly flush surface. Themagnet pole piece 26 also holds the air hammer and tappet 2'! verticalrelative to the skin Ill, assuring a smooth riveted joint.

It is to be understood that this invention has been described as usedwith an air hammer merely for illustrative purposes, as other types ofriveting processes and spot welding can be combined with the magneticbucking bar. For example, a powerful magnet of the type described wouldbe capable of squeeze riveting the small aluminum rivets commonly usedin airplane construction. The tappet 2! could be arranged as oneelectrode of a spot welding machine, the bucking bar forming the otherelectrode, while the magnet applied the necessary pressure for spotwelding. V

The bucking bar l8 and its holder I! may be tailored to fit the spaceavailable, as indicated in Figures II and III. In Figure II the holderI1 is slidable in the channel member l2 and is of a width sufiicient tocenter the line of rivets when the holder rests against the web of thechannel. A spring 29 may conveniently be used to hold the bucking baragainst the web.

In Figure III the holder 30 is formed as a flat plate slidable in thebase of the channels 3! formed by the corrugated reinforcing materialIS. the plate having upstanding guide pins 32 for a bucking bar 33 whichcan be drawn up against the rivet by the magnet 24.

In the operation of the magnetic bucking bar of this invention thematerial to be riveted is assembled and drilled for a series of rivets.In the case of flush riveting relatively thin sheets, the sheets may bedimpled to provide the desired countersink for the rivet heads, or therivet may be allowed to form its own countersink at the time it isdriven. In either case, the holder l1 and its bucking bar I8 is insertedthrough some available opening and pushed along the passage until it isin a position to back up the rivet, after which a rivet is inserted inthe hole provided therefor and the combined magnet and riveting hammerapproximately centered over the head of the rivet. Upon closing theelectric circuit energizing the magnet, the magnet pole piece 26 willattract the bucking bar I8. A subsequent operationof the air hammer willact to both seat the preformed countersunk head of the rivet, and form aflat head on the inner end thereof,

the magnetic force acting on the bucking bar l8 pulling it towards thematerial as the head forms, until the pins 2| limit further forwardmotion. In effect, the air hammer taps a series of blows on the tappet21, which is held against the surface of the skin in by the magnet polepiece 26, the effect of the blows being transmitted through the rivetshank to the bucking bar, which bounces slightly to perform the headingoperation.

It will be evident from the foregoing that the magnetic bucking bar ofthis invention can be utilized in confined places inaccessible tomanually held bucking bars and that one man can both position thebucking bar and perform the riveting heading operation.

Having thus described my invention and the present preferred embodimentthereof, I desire to emphasize the fact that many modifications may beresorted to in a manner limited only by a just interpretation of thefollowing claims.

I claim:

1. A riveting tool of the class described comprising a bucking bar,holding means for said bucking bar adapted to allow freedom of movementthereof towards the rivet to be bucked, electro-magnetic means forattracting and holding said bucking bar against the material beingriveted, said electro-magnetic means having an annular pole adapted tocontact the material ?being riveted about the rivet location therein,and rivet driving means concentrically seated within said annular poleflush with the surface thereof.

2. A riveting tool of the class described comprising a bucking bar, aguide for said bar adapted to allow freedom of movement thereof towardsthe rivet to be bucked, an electromagnet for attracting and holding saidbar against the rivet, said electromagnet having a polepiece adapted tocontact the material being riveted about the rivet location therein, ariveting mandrel extending axially through said electromagnet and.having a head of increased diameter on one end thereof, a recessed seatformed in said polepiece, said head being positioned within said seatwhen the head and the polepiece are in operative position in contactwith the material being riveted.

3. A riveting tool of the class described comprising a bucking barhaving a heading surface thereon and being adapted for progressivemovement towards the rivet being bucked as the heading thereof proceeds,a guide for said bar, said bar being guided for lateral movement in saidguide towards said rivet, means associated with said guide and bar forlimiting the extent of said movement, an electromagnet for holding saidbar against said rivet, said electromagnet having a polepiece adapted tocontact the material being riveted, a riveting mandrel extending (0;through said electromagnet and having a rivet driving head thereonconcentrically seated within said polepiece flush with the surfacethereof.

4. In a device as set forth in claim 3 wherein the rivet driving head onthe mandrel is frustoconical in form, the polepiece having a conicalseat formed therein to provide a seat for said driving head.

5. In a device as set forth in claim 3, wherein 4 the limiting meansassociated with the guide and bar comprises an extension on the bar andmeans on the guide adapted to engage said extension to limit movement ofthe bar towards the rivet.

WILLIAM RAY HOLCOMB.

